1. Technical Field
The present invention relates to a radiation image capture device, and particularly relates to a radiation image capture device in which a radiation detection panel and a signal processing board are connected by a flexible printed circuit (FPC).
2. Related Art
In recent years, radiation image detectors such as flat panel detectors (FPD) and the like have been realized. In an FPD, a radiation-sensitive layer is disposed on a thin film transistor (TFT) active matrix substrate, and the FPD is capable of converting radiation directly to digital data. A radiation image capture device that uses this radiation detector has the advantage, over prior art radiation image capture devices that use X-ray films, imaging plates and the like, that images may be continuously checked. This device also has the advantage of being able to perform radioscopic imaging (video imaging) in which radiation images are successively imaged.
Diverse types of this kind of radiation detector have been proposed. For example, a radiation detector that employs an indirect conversion system converts the radiation to light using a scintillator, converts the converted light to electronic charges with sensor portions such as photodiodes or the like, and accumulates these charges. The accumulated charges are data about an image captured by X-ray imaging. CsI:Tl, GOS (Gd2O2S:Tb) or the like is used for the scintillator. A radiation image capture device reads out the charges accumulated in the radiation detector in the form of analog signals, amplifies the analog signals with amplifiers, and then converts the analog signals to digital data with an analog-digital (A/D) converter.
The radiation detector is provided with a sensor portion and a signal processing board. The signal processing board performs driving control of the sensor portion and performs signal processing of captured image data provided from the sensor portion. The signal processing board is disposed to oppose the sensor portion, and the sensor portion and signal processing board are connected using a flexible printed circuit.
Portable radiation image detectors (electronic cassettes) are in high demand because of their ease of handling. Japanese Patent Application Laid-Open (JP-A) No. 2010-264250 discloses an X-ray imaging device that detects when irradiations of radiation start and stop and the like, and that does not require control for synchronization with radiation generation timings. In association with adjustments of position and posture of an imaging subject (a patient) during and before X-ray imaging, this kind of X-ray imaging device is subjected to contact with the imaging subject and impacts and the like. At such times, the flexible printed circuit touches or rubs against an interior wall of a casing that accommodates the sensor portion and the signal processing board, electrostatic charging occurs at wiring of the flexible printed circuit, and counter (compensation) charges are produced. These counter charges cause changes in the analog signals being propagated in the wiring of the flexible printed circuit, leading to misdetections of the captured X-ray image data. In a flexible printed circuit at which amplifiers are mounted, analog signal charges that have not yet been converted to analog signal voltages by the amplifiers are vulnerable to the effects of electrostatic charging.
Similarly, in an X-ray imaging device that requires control for synchronization with radiation generation timings, if electrostatic charging occurs at wiring in a flexible cable, there are changes in the analog signals during a readout of captured X-ray image data. These changes in the analog signal appear as noise in captured X-ray images.
JP-A No. 5-259591 discloses a flexible printed circuit in which a copper layer is applied to a plastic film, and a flexible printed circuit in which an antistatic layer is formed on a plastic film and the antistatic layer is covered with a protective layer. These flexible printed circuits are useful in regard to suppressing electrostatic charging.
However, in the above-mentioned flexible printed circuit in which a copper layer is applied, the copper layer detaches if it touches the casing, and it is hard to maintain the electrostatic charging suppression effect. This detachment is less likely if the thickness of the copper layer is increased, but an increase in thickness of the copper layer increases stiffness and impairs the flexibility of the flexible printed circuit.
Further, in the above-mentioned flexible printed circuit in which an antistatic layer is formed, the decay time of electrostatic charges is long, and the charges act as stray capacitances on the wiring. The stray capacitances cause changes in the analog signals being propagated in the wiring of the flexible printed circuit, leading to misdetections of captured X-ray image data. The stray capacitances also cause changes in time constants, leading to delays of the analog signals being propagated in the wiring.